This invention relates to rims for a tire testing machine and more particularly the invention relates to a rim whose contour is stepped to provide multiple bead seats to permit the testing, on one set of rims, of tires having differing bead diameters.
A tire has two beads that engage spaced bead seats of a contoured tire rim. Upon inflation, the beads form an airtight seal with the bead seats that holds the air in the tire at the inflation pressure.
Tires are manufactured in various sizes. The bead diameters have been standardized in 1" steps, as, for example, 13", 14", and 15" diameter beads. Similarly, the contour of the rim in the area of the bead seat has been standardized, and these standards have been published by the Tire and Rim Association, Inc. As will be seen hereafter, the bead seat per se is contoured precisely as is the immediately adjacent rim area that is contacted by the side wall inflation bulge immediately adjacent the tire bead.
Tire testing machines have two rim halves that are spaced apart. These halves are hydraulically brought together with a tire between the two halves. See U.S. Pat. No. 4,852,398. When the tire is in position between the two rim halves, the tire is inflated. Thereafter, it is rotated against a road wheel (sometimes load wheel) to simulate road conditions. Run out, lateral, and radial force variations are measured by the tire testing apparatus.
It is very important that the rim halves, when together, replicate the standard bead seat and inflation bulge contours. This substantially exact replication is necessary in order for the results produced by the tire testing machine to be meaningful in relation to the actual vehicle tire rims onto which the tires are to be mounted.
In tire testing machines, it would be desirable to use one set of rim halves for multiple bead diameters, e.g., 13", 14", and 15". But the rims cannot have, on one rim, seats for two adjoining bead diameters, e.g., 13" and 14". The bead seats per se can be contoured for adjoining bead diameters, but a tire seated on the smaller bead seat would not have the right contour immediately adjacent the bead to resist the inflation bulge. Where there should be a proper contour to resist the inflation bulge, there is instead the bead seat for the next larger tire.